would like to learn how to use gfx library on Android studio



which one's better



or any other one better?

The primary purpose of libgdx is to be able to write code that compiles down to run on multiple phones.

I have used it for a couple small game projects. It is pretty straightforward and easy to learn. As long as you don't need to do anything with phone hardware (accelerometer, etc), you don't really have to write any OS specific code.

anf wat about open GL?

libgdx uses opengl. the only reason you'd write low level opengl is if you want to create a graphics engine for yourself which is 10x more work than just using an already available engine like libgdx